Method for producing a shaped component having at least two structural regions of different ductility

ABSTRACT

According to the method, a blank ( 7 ) that is severed from strip material ( 4 ) of coated, high-strength boron steel is homogeneously heated in a furnace ( 11 ) having a plurality of temperature zones ( 8, 9, 10 ) first in a 1 st  zone ( 8 ) to a temperature of approximately 830° C. to 950° C. and maintained at this temperature level for a defined time (t). Thereafter, a region ( 12 ) of first kind of the blank ( 7 ) is cooled down in a 2 nd  zone ( 9 ) of the furnace ( 11 ) to a temperature of approximately 550° C. to 700° C. and maintained at this lowered temperature level for a defined time (t 1 ). At the same time, a region ( 13 ) of second kind of the blank ( 7 ) is maintained in a 3 rd  zone ( 10 ) of the furnace ( 11 ) at a temperature level of approximately 830° C. to 950° C. during a time (t 2 ). After this heat treatment, a blank ( 7 ) is formed into a shaped component ( 1 ) in a thermoforming process.

The invention relates to a method for producing a shaped component with at least two structural regions of different ductility from a metallic blank that has been cut from strip material, whereby the blank has differently heated regions and then undergoes a thermoforming process to form it into the shaped component (preamble of claims 1, 2, 3).

DE 102 56 621 B3 describes a method for producing a shaped component with at least two structural regions of different ductility, and a continuous furnace for this method. According to this proposal, a semi-finished product of hardenable steel moves through a continuous furnace with at least two zones having different temperature levels and arranged side-by-side in movement direction. The semi-finished product is hereby heated to different temperatures so as to establish two structural regions of different ductility during a subsequent thermoforming process.

DE 102 08 216 C1 also discloses a method for producing a shaped component with at least two structural regions of different ductility. A semi-finished product of hardenable steel moves hereby through a heating device with homogenous temperature distribution and is heated completely to an austenitization temperature. A partial region of first kind of the semi-finished product is then cooled down during its further transport that the base material can convert from austenite to ferrite and/or perlite. Thus, a subsequent thermoforming process does not cause any or causes only little martensitic formation. As a result, the partial region of first kind has a high ductility. At the same time, the other partial region of second kind of the semi-finished product is subjected during the transport to a temperature which is held at a level to allow the formation of just enough martensitic structures during the subsequent thermoforming process. Thus, compared to the partial region of first kind, the partial region of second kind has a smaller ductility but greater strength.

Even though heating is carried out in a furnace under a nitrogen atmosphere in both afore-described methods, scaling cannot be avoided of the respective semi-finished product during transfer from the furnace to a forming press and also during the forming process.

Starting from the state of the art, the invention is based on the object to provide a method for the production of a shaped component with at least two structural regions of different ductility, which method obviates problems associated with scaling.

The first solution of the object which the invention is based upon is set forth by the features of claim 1.

Accordingly, when applied for a shaped component of high-strength boron steel coated with an Al/Si coating, a blank cut from strip material of such a substance is completely homogenously heated first to such a temperature and maintained at this temperature level for a defined time that a diffusion layer as corrosive or scale protective layer is formed, wherein material from the coating diffuses into the base substance. The heating temperature is about 830° C. to 950° C., preferably about 920° C. This homogenous heating is carried out advantageously in a 1^(st) zone of a continuous furnace which has several temperature zones. Following this method step, a region of first kind of the blank is cooled down in a 2^(nd) zone of the furnace to a temperature which causes austenite to break down. This takes place at about 550° C. to 700° C., preferably at about 625° C. This lowered temperature level is maintained for a defined time so that the break down of austenite is reliably implemented.

Simultaneous with the local cool down of the region of first kind of the blank, the temperature in a region of second kind is maintained in a 3^(rd) zone just enough to allow formation of martensitic structures during the subsequent thermoforming in a respective press. This temperature is at 830° C. to 950° C., preferably at about 900° C.

In this way, the regions of first and second kinds of the shaped component have different ductility properties, with the region of second kind, compared to the region of first kind, having a smaller ductility but yet higher strength properties.

Such shaped components manufactured in this way, can have concrete sections that can be best suited to the demands at hand in order to meet its characteristic as structural component, for example as component of a vehicle body.

A second solution of the object which the invention is based upon is set forth by the features of claim 2.

The formation of a diffusion layer as corrosive or scale protective layer is hereby realized by alloying strip material from high-strength boron steel, coated with an Al/Si coating, in a first operating step during continuous advance through a pre-furnace and then cooling it down. The temperature is 830° C. to 950° C., preferably about 920° C.

Blanks are then severed in a further operating step from this alloyed strip material. Subsequently, each severed blank is transferred into a two-zone furnace. A region of second kind of the blank is hereby austenitized at a temperature of 830° C. to 950° C., preferably about 930° C. The region of first kind is heated to a temperature which at a maximum is below the austenitization temperature which is about 550° C. to 700° C., preferably about 680° C.

This type of heat treatment causes the regions of second kind of the shaped components ultimately manufactured in a thermoforming process from the blanks to have smaller ductility properties, compared to the regions of first kind, but, yet have higher strength properties.

A third solution of the object which the invention is based upon is set forth by the features of claim 3.

Accordingly, when applied for a shaped component of high-strength boron steel coated with an Al/Si coating, blanks are cut from strip material of such a substance. Thereafter, each blank is homogenously heated in a second operating step in a pre-furnace to a temperature of about 830° C. to 950° C., preferably about 920° C., maintained at this temperature level for a defined time, and then cooled down again. Formation of a diffusion layer as corrosive or scale protective layer is hereby realized from the Al/Si coating of the strip material. In a third operating step, each blank is then transferred to a two-zone furnace and a region of first kind is again heated in a 1^(st) zone of the furnace to a temperature of about 550° C. to 700° C., preferably about 680° C. At the same time, a region of second kind is heated in a 2^(nd) zone of the furnace to a temperature of 830° C. to 950° C., preferably about 920° C. Finally, the blank is formed by a thermoforming process into a shaped component. The shaped component has then a region of second kind which, compared to the region of first kind, has smaller ductility properties but higher strength properties.

To accelerate cooling down to the transformation temperature, at which austenite breaks down to ferrite and perlite, according to the features of claim 4, the local cool down of the region of first kind of the blank can be realized after heating by contacting the region of first kind momentarily with cooling jaws.

According to the features of claim 5, it is, however, also possible to blow cooled gas onto the region of first kind of the blank after heating.

This can be preferably implemented by using nitrogen as gas, as set forth in claim 6. Exemplified embodiments of the invention will now be described in greater detail with reference to the drawings, which show in:

FIG. 1 a schematic illustration of the production of a shaped component with two structural regions having different ductility;

FIG. 2 a schematic illustration of a further method for the production of a shaped component with two structural regions having different ductility; and

FIG. 3 a schematic illustration of a third method for the production of a shaped component with two structural regions having different ductility.

1 designates in FIGS. 1 to 3 a shaped component with two structural regions 2, 3 of different ductility. The shaped component 1 involves a B column of an otherwise unillustrated vehicle body.

The manufacture of the shaped component 1 is based on high-strength boron steel which is provided with an Al/Si coating.

A strip material 4 from such steel is wound according to FIG. 1 to a coil 5. The strip material 4 is then drawn continuously from this coil 5 and guided through a punch 6. Blanks 7 are cut from the strip material 4 in the punch 6 and then fed to a continuous furnace 11 having three temperature zones 8, 9, 10.

In a 1^(st) zone 8 of the continuous furnace 11, each blank 7 is completely homogenously heated to a temperature of about 830° C. to 950° C., preferably 920° C., and maintained at this temperature level over a defined time t (FIG. 2).

Subsequently, a region 12 of first kind of the blank 7 is cooled down in a 2^(nd) zone 9 of the continuous furnace 11 to a temperature of about 550° C. to 700° C., preferably about 680° C., cooled down and maintained at this lowered temperature level over a defined time t₁. At the same time, a region 13 of second kind of the blank 7 is maintained in a 3^(rd) zone 10 of the continuous furnace 11 at a temperature level of about 830° C. to 950° C., preferably about 900° C.

After exiting the continuous furnace 11, the heat-treated blank 7 is thermoformed into the shaped component 1 in a press not shown in greater detail.

Illustrated below and above the continuous furnace 11 is the temperature profile as a function of the time during passage of the blank 7 through the continuous furnace 11 with respect to the region 12 of first kind and the region 13 of second kind of the blank 7, with the lower graph 14 depicting the heat treatment of the region 12 of first kind, i.e. the temperature profile of the “soft” section of a blank 7, and the upper graph 15 depicting the heat treatment of the region 13 of second kind, that is the temperature profile of the “hardened” section of a blank 7.

FIG. 2 shows a method for the production of a shaped component 1 with two structural regions 2, 3 of different ductility, whereby strip material 4 of boron steel provided with an Al/Si coating is first drawn from a coil 5 and guided through a pre-furnace 16. The strip material 4 is homogenously heated in the pre-furnace 16 to a temperature of about 830° C. to 950° C., preferably about 920° C., and maintained at this temperature level over a defined time. The thus heat-treated strip material 4 is then wound to a coil 17. The heat-treated strip material 4 is fed from this coil 17 to a punch 18 for cutting blanks 7 from the strip material 4. The strip material 4 may also be cooled down directly after exiting the pre-furnace 16 and then fed to the punch 18. These blanks 7 from the pre-treated strip material 4 are then transferred to a two-zone furnace 19 and a region 12 of first kind is heated therein in a 1^(st) zone 20 of the furnace 19 to a temperature of about 550° C. to 700° C., preferably about 680° C., and a region 13 of second kind is heated simultaneously in a 2^(nd) zone 21 of the furnace 19 to a temperature of about 830° C. to 950° C.

The blanks 7 heat-treated in this manner are ultimately formed into shaped components 1 with two different structural regions 2, 3 by way of a thermoforming process not shown in greater detail.

The lower graph 22 in the temperature-time diagram 23 of FIG. 2 shows in this context the temperature profile in the region 12 of first kind of the blank 7, and the upper graph 24 shows the temperature profile in the region 13 of second kind of each blank 7.

FIG. 3 illustrates the manner in which the strip material 4 of boron steel provided with an Al/Si coating is drawn from a coil 5 and directly fed to a punch 18. Blanks 7 are cut from the strip material 4 in the punch 18 and then fed to a pre-furnace 16 for homogenously heating the blanks 7 to a temperature of about 830° C. to 950° C., preferably about 920° C., and maintained at this temperature level over a defined time t₂.

Blanks 7 heat-treated in this way are then transferred to the afore-mentioned two-zone furnace 19 and a region 12 of first kind is heated here, as described, in the 1^(st) zone 20 to a temperature of about 550° C. to 700° C., preferably about 680° C., and a region 13 of second kind is heated at the same time in the 2^(nd) zone 21 of the furnace 19 to a temperature of about 830° C. to 950° C.

The temperature-time diagram 23 corresponds to the one of FIG. 2.

Also the thus heat-treated blanks 7 are finally formed into shaped components 1 with two different structural regions 2, 3 by way of a thermoforming process.

REFERENCE SYMBOLS

1—shaped component

2—structural region of 1

3—structural region of 1

4—strip material

5—coil

6—punch

7—blank

8—1^(st) zone of 11

9—2^(nd) zone of 11

10—3^(rd) zone of 11

11—continuous furnace

12—region of first kind of 7

13—region of second kind of 7

14—lower graph

15—upper graph

16—pre-furnace

17—coil

18—punch

19—two-zone furnace

20—1^(st) zone of 19

21—2^(nd) zone of 19

22—lower graph in 23

23—diagram

24—upper graph in 23

t—time

t₁—time

t₂—time 

1.-6. (canceled)
 7. A method of producing a shaped component with at least two structural regions of different ductility, comprising the steps of: cutting a blank from a strip material of high-strength boron steel provided with an Al/Si coating; heating the blank in a first temperature zone of a furnace to a first temperature of about 830° C.-950° C.; maintaining the blank at the first temperature for a defined time; allowing a first region of the blank to cool down in a second temperature zone of the furnace to a second temperature of about 550° C.-700° C.; maintaining the first region of the blank at the second temperature for a defined time, while maintaining a second region of the blank in a third temperature zone of the furnace at the first temperature; and forming the blank into the shaped component in a thermoforming process.
 8. The method of claim 7, wherein the first region of the blank is brought momentarily in contact with cooling jaws to cool down to the second temperature.
 9. The method of claim 7, wherein the first region of the blank cooled down to the second temperature by blowing cooled gas onto the first region.
 10. The method of claim 7, wherein the cooled gas is nitrogen.
 11. A method of producing a shaped component with at least two structural regions of different ductility, comprising the steps of: heating a strip material of high-strength boron steel provided with an Al/Si coating in a pre-furnace to a first temperature of about 830° C.-950° C.; maintaining the strip material at the first temperature for a defined time; cooling down the strip material; cutting blanks from the strip material; transferring each blank into a two-zone furnace; heating a first region of each blank in a first zone of the furnace to a second temperature of about 550° C.-700° C., while heating a second region in a second zone of the furnace to the first temperature; and forming the blanks into the shaped component in a thermoforming process.
 12. The method of claim 11, wherein the first region of the blank is brought momentarily in contact with cooling jaws to cool down to the second temperature.
 13. The method of claim 11, wherein the first region of the blank cooled down to the second temperature by blowing cooled gas onto the first region.
 14. The method of claim 13, wherein the cooled gas is nitrogen.
 15. A method of producing a shaped component with at least two structural regions of different ductility, comprising the steps of: cutting blanks from a strip material of high-strength boron steel provided with an Al/Si coating; heating each blank to a first temperature of about 830° C.-950° C. in a pre-furnace; maintaining the blanks at the first temperature for a defined time; cooling down the blanks; transferring each blank into a two-zone furnace; heating a first region of each blank in a first zone of the furnace to a second temperature of about 550° C.-700° C., while heating a second region in a second zone of the furnace to the first temperature; and maintaining the first and second regions of each blanks at the first and second temperatures, respectively; forming the blanks into the shaped component in a thermoforming process.
 16. The method of claim 15, wherein the first region of the blank is brought momentarily in contact with cooling jaws to cool down to the second temperature.
 17. The method of claim 15, wherein the first region of the blank cooled down to the second temperature by blowing cooled gas onto the first region.
 18. The method of claim 17, wherein the cooled gas is nitrogen. 